The output of an ion discharge chamber consists of many species in addition to the contamination produced by sputtering from its walls. Thus a mass separator is required to make source pure. The mass separation is based on the dynamics of charged particles, of mass (m) and velocity (v), moving at right angles to a uniform magnetic field (a flux density of B). These particles will experience a force (F) such that . This force tends ions to move in a circular path of radius r, and experience a centrifugal force. These forces are equal and opposite. The velocity of ions is related to the accelerating potential (V) by . Combining these equations, the radius of the ion path is given as .